[Dotnet] Fix failing test "install_dotnet_lts"

[samruddhikhandale]

          @gauravsaini04 Can you prioritize and help fix https://github.com/devcontainers/features/actions/runs/9490744002/job/26193280306?pr=997#step:4:2676 tests? Thanks!

Originally posted by @samruddhikhandale in #997 (comment)

[prathameshzarkar9]

Hi @samruddhikhandale ,

from resources it is found that , as of now, there is no .NET 8.0.302 designated as an LTS version. The latest LTS version is .NET 6.0. If .NET 8.0 were to become LTS in the future, it would be reflected in the URL: https://dotnetcli.azureedge.net/dotnet/Sdk/**LTS**/latest.version
whereas , $channel = "LTS"
output : 8.0.301

However, at present, there is no LTS version 8.0.302 available to retrieve the latest version of the dotnet.

I found one fix to pass the test case install_dotnet_lts as below.
when I changed the $channel = 8.0 , it is correctly retrieving the latest version of dotnet 8.0.302
the url will be: https://dotnetcli.azureedge.net/dotnet/Sdk/**8.0**/latest.version

PR is created here: #1003